1. Field of the Invention
The present invention relates to a liquid ejecting head for ejecting liquid using a bubble formed by applying thermal energy to the liquid, a method for ejecting liquid using the same, and a method for manufacturing the liquid ejecting head.
In addition, the present invention can be applied to various apparatuses, such as a printer, a copying machine, facsimile machines having a communication system, and a word processors having a printing portion, which perform recording on recording media, such as paper, thread, fiber, textile, leather, metal, plastic, glass, wood, and ceramic, and can also be applied to industrial recording equipment functionally combined with various processing apparatuses.
In the present invention, xe2x80x9crecordingxe2x80x9d not only means that meaningful images such, as letters and figures, are input on a recording medium but it means that meaningless images such as patterns are input thereon.
2. Description of the Related Art
In liquid ejecting heads which have been used in practice, an ejection element (for example, an electro-thermal transducer used for forming a bubble or a piezoelectric element which is displaced or deformed) driven for ejecting a liquid droplet is disposed at a position corresponding to an ejecting outlet. When this ejection element is driven, a liquid droplet to be ejected is formed by the generation of a pressure wave or a liquid flow which moves the liquid toward the ejecting outlet, and in addition, a pressure wave or a liquid flow toward a liquid chamber is also generated for refilling the liquid in the ejection element. This liquid chamber may be used as a common liquid chamber when a plurality of liquid flow paths, each provided with an ejection element and an ejecting outlet, is arranged to communicate with this chamber.
A pressure wave or a liquid flow toward this liquid chamber or the common liquid chamber is collectively called as xe2x80x9ca backwavexe2x80x9d and may interfere with the refilling or may impose a meniscus vibration component on adjacent ejecting outlets in some cases. A number of inventions focusing on this xe2x80x9cbackwavexe2x80x9d have been proposed, and among those mentioned above, constituent elements, such as a member (membrane, valve, or the like) for blocking or absorbing a backwave, provided in a liquid flow path having an ejection element and an ejecting outlet have been frequently proposed. For example, according to the invention disclosed in Japanese Unexamined Patent Laid-Open No. 6-31918 (specifically, see FIG. 3), a flat and triangular-shaped member is disposed so that the corner of the triangle opposes a heater used for generating a bubble. In this invention, this flat member temporarily and slightly reduces the backwave. However, since the relationship between the triangular shape and the growth of a bubble has not been mentioned and has not been considered, the invention described above has the following problems.
That is, according to the invention disclosed in the publication described above, since the heater is disposed at the bottom of a recess portion and is not allowed to linearly communicate with the ejecting outlet, the form of liquid droplet cannot be stable. In addition, since bubbles are allowed to grow at the periphery of the corner of the triangle shape, the bubbles grow from one side of the flat and triangle-shaped member to the entire opposite side thereof, and as a result, the general growth of bubbles is complete in the liquid as if the flat member has not been disposed. Accordingly, the bubbles thus grown have not been affected by the presence of the flat member at all. In contrast, since the entire flat member is surrounded by bubbles, when the bubbles contract, the refilling to the heater disposed in the recess generates a turbulent flow, thereby forming minute bubbles in the recess. As a result, the primary object to eject liquid by the growth of a bubble cannot be achieved satisfactorily.
In addition, according to EP Laid-Open No. 436047A1, an invention is proposed in which a first valve, which is provided between an area in the vicinity of an ejecting outlet portion and a bubble generating region so that these portions are blocked from each other, and a second valve, which is provided between the bubble generating region and an ink supplying portion so that these portions are completely blocked from each other, are alternately opened and closed (specifically, see FIGS. 4 to 9 of EP Laid-Open No. 436047A1). However, according to this invention, since these three portions are divided into two parts by the valve operation described above, ink following a liquid droplet when it is ejected will make a long trail, and satellite dots will be increased compared to the general ejecting method in which bubble growth, contraction, and defoaming are sequentially performed (the reason for this is considered that the effect of meniscus recession caused by defoaming may not be used). In addition, during refilling, liquid is supplied to the bubble generating region while bubbles are being defoamed; however, since liquid is not supplied to the vicinity of the ejecting outlet until subsequent bubble generation occurs, liquid droplets ejected vary considerably, and in addition, response frequency for ejection is extremely small. As a result, the proposal described above cannot be used practically.
A number of inventions each using a movable member (for example, a flat member having a free end closer to an ejecting outlet side than the fulcrum), which can effectively improve liquid ejecting properties and are completely different from the conventional techniques described above, has been proposed by the inventors of the present invention. Among the inventions described above, Japanese Unexamined Patent Laid-Open No. 9-48127 discloses an invention in which the upper limit of displacement of a movable member is controlled to make the movable member move strictly as it is designed. In addition, Japanese Unexamined Patent Laid-Open No. 9-323420 discloses an invention in which the position of a common liquid chamber at an upstream side with respect to the position of the movable member is shifted to that of the free end side thereof, that is, to the downstream side, by using the advantages of the movable member in order to improve the refilling ability.
In addition, in Japanese Unexamined Patent Laid-Open No. 10-24588, an invention focusing on bubble growth caused by pressure wave propagation (acoustic wave) as a factor of liquid ejection is disclosed in which a part of the bubble generating area is free from the movable member described above. In addition, for example, in Japanese Unexamined Patent Laid-Open No. 2000-621845, a technique is disclosed in which, by analyzing the process from the bubble generation to defoaming in detail in view of the formation of liquid droplets to be ejected, specific printing quality obtained by an inkjet device is decreased, satellite dots which contaminate a device itself or a recording medium are decreased, the refilling can be performed at a high speed, the vibration of meniscus can be quickly converged, and the image quality can also be obtained stably during continuous ejection process.
In addition, a bimetal method in which ideal switching of the movable member or the valve unit described above is performed by independent driving without being dependent on the behavior of an ejection element has been disclosed in Japanese Unexamined Patent Laid-Open No. 9-131891. In this publication, a liquid flow path forms a single head, and a valve completely blocks a connection portion between the liquid flow path and a liquid chamber as shown in FIG. 8. In another example of this publication, a plurality of bimetals which are driven by displacement in a single liquid flow path has been disclosed. According to this publication, wires and electrical power are necessary for driving switching bimetals, and hence, this invention is difficult to apply a liquid ejecting head containing a number of liquid flow paths.
As described above, the properties of each liquid flow path have been improved by the conventional structure; however, influences between a plurality of liquid flow paths have not been seriously considered.
In consideration of these technical problems described above, the advantages and disadvantages of conventional movable members such as valves were reevaluated, and novel and effective functions/actions were pursed by forming new movable members in order to realize a liquid ejecting head which can reduce back wave generation, has a hybrid structure composed of a plurality of liquid flow paths, and in addition, can perform refilling at a high speed even while continuous ejection is being performed. Through this intensive research by the inventors of the present invention, an invention for improving in mechanical strength of a fulcrum portion of a movable member, an invention focusing on the arrangement of movable members, an invention for reducing crosstalks between adjacent liquid flow paths in a common liquid supply chamber region by using a plurality of movable members, and the like were made.
To these ends, a liquid ejecting head according to one aspect of the present invention is provided which comprises a member provided with a plurality of ejecting outlets for ejecting liquid; s substrate having a plurality of bubble generating means which generates thermal energy for generating and growing a bubble used for ejecting the liquid, the bubble generating means opposing the associated ejecting outlet; a plurality of liquid flow paths each of which communicates with the associated ejecting outlet and has a bubble generating region for generating the bubble in the liquid by the thermal energy; a liquid supply inlet which is a long through-hole formed in the substrate; a common liquid supply chamber which communicates with the plurality of said liquid flow paths via the liquid supply inlet and which supplies liquid to the plurality of said liquid flow paths via the liquid supply inlet; and a plurality of movable members disposed in the longitudinal direction of the liquid supply inlet so as to cover the liquid supply inlet, each of the movable members having a free end in the associated liquid flow path and being supported above the liquid supply inlet with a minute spacing therebetween.
In a method for ejecting liquid by using a liquid ejecting head in accordance with another aspect of the present invention, the liquid ejecting head comprises a member provided with a plurality of ejecting outlets for ejecting liquid; a substrate having a plurality of bubble generating means which generates thermal energy for generating and growing a bubble used for ejecting the liquid, the bubble generating means opposing the associated ejecting outlet; a plurality of liquid flow paths each of which communicates with the associated ejecting outlet and has a bubble generating region for generating the bubble in the liquid by the thermal energy; a liquid supply inlet which is a long through-hole formed in the substrate; a common liquid supply chamber which communicates with the plurality of said liquid flow paths via the liquid supply inlet and which supplies liquid to the plurality of said liquid flow paths via the liquid supply inlet; and a plurality of movable members each disposed in the associated liquid flow path so as to cover the liquid supply inlet with a minute spacing therebetween, the movable member having a free end and a supporting portion, the free end being provided so as not to overlap the bubble generating region. The method for ejecting liquid mentioned above comprises a step of substantially blocking the liquid supply inlet without contacting the bubble.
In addition, in a method for manufacturing a liquid ejecting head in accordance with another aspect of the present invention, the liquid ejecting head comprises a plurality of ejecting outlets for ejecting liquid; a plurality of liquid flow paths each of which always communicates with the associated ejecting outlet at one end of the liquid flow path and which has a bubble generating region for generating a bubble in the liquid; bubble generating means which generates thermal energy for generating and growing the bubble; a substrate having the bubble generating means; a liquid supply inlet which communicates with the plurality of said liquid flow paths and which is a long through-hole formed in the substrate; and a plurality of movable members each having a free end and being supported above the liquid supply inlet at the liquid flow path side with a minute spacing therebetween. The method for manufacturing the liquid ejecting head described above comprises a step of forming a membrane layer on the substrate in an area at which the liquid supply inlet is formed; a step of providing the bubble generating means and the movable members on the substrate; a step of forming a liquid flow path pattern for forming the plurality of said liquid flow paths on the substrate provided with the bubble generating means and the movable members; a step of applying a material for forming walls of the liquid flow paths so as to cover the liquid flow path pattern; a step of performing anisotropic etching of the substrate from the rear side thereof which is opposite to the side on which the movable members are formed; a step of removing the membrane layer provided in the area at which the liquid supply inlet is formed by dry etching using the liquid flow path pattern as an etching stopper film for forming a through-hole used as the liquid supply inlet; and a step of removing the liquid flow path pattern.
Since the liquid ejecting head in accordance with the present invention has the structure described above, pressure waves generated by bubble growth in bubble generating regions are not propagated to a liquid supply inlet side and other liquid flow paths, and most of the pressure waves move toward ejecting outlet sides, whereby ejecting power can be significantly increased.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments (with reference to the attached drawings).